1. Field Of The Invention
The present invention relates generally to an automatic transmission primarily intended for motor vehicle use and, more particularly, to a sensing system for generating codes which represent the position of a manual gear select lever in an automatic transmission.
2. Description Of Related Art
In recent years, advanced forms of transmission control have been proposed which offer the possibility of enabling an automatic transmission to adapt itself to changing conditions. In this regard, U.S. Pat. No. 3,956,947, issued on May 18, 1976 to Leising, et al, sets forth a fundamental development in this field. Specifically, this patent discloses an automatic transmission design which features an "adaptive" control system that includes electronically operated solenoid-activated valves for controlling certain fluid pressures.
Currently, there exists a comprehensive four-speed automatic transmission system which features fully adaptive electronic control. A thorough discussion of such a transmission control system is contained in U.S. Pat. No. 4,998,450 issued on Mar. 12, 1991 to Nogle and entitled "Neutral Start Switch To Sense Shift Lever Position", which is commonly owned by the assignee of the present application. This patent is hereby incorporated by reference. The transmission control system includes a microcomputer-based controller which receives input signals indicative of engine speed, turbine speed, output speed (vehicle speed), throttle angle position, brake application, predetermined hydraulic pressures, driver selected gear and operating conditions (PRNODDL), engine coolant temperature, and/or ambient temperature. This controller generates command or control signals for causing the actuation of a plurality of solenoid-actuated valves which regulate the application and release of pressure to and from the frictional units of the transmission system.
The above transmission control system further discloses a neutral start switch for sensing the position of a manually operated shift lever to select between a plurality of predetermined operating modes. With reference to FIGS. 4B and 19 of the Nogle patent, a plate member moves in response to a shift lever and provides a cam surface at the edge with electrically conductive and non-conductive areas. A pair of separate sensors are mounted in the transmission such that an electrical contact pin of each sensor communicates with the cam surface. The signal from the electrical contact pin of each sensor combine to generate a binary code indicative of the shift lever position. Each sensor has a first contact and a second contact. The first contact travels on the cam surface while the second contact closes whenever the first contact is extended within a groove. However, this technique eliminates some of the possible binary code combinations since the first contact generally does not conduct with the second contact closed. As a result, changes between some of the manual shift lever operating positions involve single bit changes between the respective binary code combinations.
It is therefore an object of the present invention to provide for an improved sensing system which generates binary codes in response to the position of the manual gear select lever in an automatic transmission.
In particular, it is one object of the present invention to provide for a sensing system which generates combinations of binary codes which require two or more bit changes between any selected operating modes.
It is another object of the present invention to provide for improved transition codes between the operating modes of the transmission.
It is a further object of the present invention to provide for an easily installable sensing unit which has low manufacturing tolerance and good electrical contact sensing capability.